The present invention relates to suspension fittings for motor vehicle exhaust systems, and to vehicles fitted therewith.
More particularly, the invention relates to a suspension fitting for a motor vehicle exhaust system, the fitting comprising a rigid top strength member suitable for being secured to the bodywork of the vehicle and a rigid bottom strength member suitable for being secured to an exhaust system which extends longitudinally in a general direction parallel to a first axis, these two strength members being connected to each other by a resilient unit made of elastomer and comprising:
firstly a central support arm adapted to support traction forces along a second axis and to filter and damp relative vibratory motion between the top and bottom strength members, said support arm being disposed perpendicularly to the first axis and extending at an angle between a top secured to the top strength member and a bottom secured to the bottom strength member, said angle being relative to the second axis and relative to a third axis that is perpendicular to the first and second axes, the support arm extending in a first direction along the third axis from its top to its bottom; and
secondly a flexible limiting ring surrounding the support arm and connected to the two strength members to limit relative travel of said strength members in a direction corresponding to the support arm lengthening.
A suspension fitting of this type is known, in particular from document FR-A-2 761 730. It gives general satisfaction from the functional point of view, but it is expensive to make because of its complexity.
The present invention seeks in particular to mitigate this drawback of prior art suspension fittings, by proposing a fitting which reconciles all operating requirements, and which can be manufactured simply and at lower cost.
To this end, the suspension fitting of the invention comprises only a single support arm and the top and bottom strength members include respective rigid limbs placed facing each other along the third axis so as to come into abutment against each other to limit relative travel of the bottom strength member relative to the top strength member along the third axis in a second direction opposite to the first direction.
By means of these dispositions, because of a presence of a single support arm and the presence of abutments of simple design, a fitting is obtained that is of low cost, presenting excellent characteristics in filtering vibration, in particular because of relatively low stiffness along the third axis, while conserving effective limitation of travel along said third axis.
This suspension fitting is particularly effective when it is used in pairs mounted in opposition.
In advantageous embodiments, use can be made of one or more of the following dispositions:
the limbs of the two strength members correspond mutually over a certain overlap width greater than 2 centimeters (cm) measured along the first axis, and said limbs are disposed so that said overlap width is still at least 2 cm after relative displacement through 1 cm along the first axis;
the limb of the bottom strength member is of a width along the first axis that is less than the width of the limb of the top strength member along the first axis;
the limbs of the top and bottom strength members are covered in a layer of elastomer that is integral with the elastomer of the support arm and of the limiting ring;
the respective limbs of the strength members come into abutment against respective horizontal portions of the other strength members in a direction corresponding to the support arm being compressed along the second axis;
the limb of the top strength member comes into abutment against the bottom of the support arm in the first direction along the third axis;
the flexible limiting ring is adapted to enter into resonance at a frequency lying in the range 250 hertz (Hz) to 350 Hz to diminish the dynamic stiffness of the fitting in the vicinity of said frequency; and
the flexible limiting ring is provided on its peripheral surface with a plurality of notches.
In another aspect of the invention, it provides a vehicle having bodywork and an exhaust system connected to the bodywork via at least one suspension fitting as defined above.
Advantageously, the exhaust system is connected to the bodywork via at least two fittings mounted in opposition, the respective flexible rings thereof being disposed in two sloping planes that converge downwardly towards each other.